Identification of Group A Streptococci

Abstract

The fluorescent-antibody technique for identifying group A streptococci was compared with a standard precipitin method. When employedafter isolation on blood agar, definite agreement between the two techniques was obtained in 174 of 203 instances. Evaluation ofprimary identification by the fluorescent-antibody techniqueshowed agreement in 189 of 205 instances, but analysis of the 33 specimen pairs in which group A streptococci were identified by one or both techniques revealed agreement in only 17 instances. Primary isolation on a blood agar plate, followed by group identification by one of several available techniques, has the advantages of an easy method of screening out negative specimens and of providing quantitative information on positive specimens. These advantages seem to outweigh those of the more rapid but probably less definitive method of primary identification by the fluorescent-antibody technique.